Template improvements for aggregation filter

[benwalch]

Q	A
Bug report?	no
Feature request?	yes
BC Break report?	no
RFC?	no

The following proposed changes should provide more flexibility in structuring templates and views for the aggregation filter

• Each configured filter should have its own template view. The view should be identified by the filter's name. If no corresponding template can be found, the general template (aggregation.html.twig) should be loaded which provides full backward compatibility.
• The filters array available in the view should be associative, where the key is the configured filter's name. Thereby a specific filter can be accessed in the view more easily. BC is provided here since the general aggregation template iterates over the filter array, regardless of the keys.
• The name of configured filter should be accessible in the view.

[benwalch]

proposal two (filter array associative in view) cannot be solved here. Moved to https://github.com/dachcom-digital/pimcore-dynamic-search/issues/49